Is there a keyboard shortcut I can use to make a window occupy the left or right half of the screen? I'm using a modified version of Ubuntu. On Mac I just use Divvy but I'm not sure if there is a Linux tool to do the same thing.

If you are the kind of guy who likes to partition your screen up into increments like full screen and half screen using keyboard shortcuts, you might consider using a different window manager entirely. I don't think there is any reason you have to stay with the whole Gnome/Metacity/Compiz scene.

There are a plethora of Window Managers available for Linux that have different philosophies about how they handle windows. Personally I am sold on using framework or tiling window layouts rather than the traditional floating model. There are several WM's that support mix-modes as well. I use awesome and love how flexible it is particularly with being scriptable and it's handling of multiple monitors. There are similar ones such as dwm and xmonad as well.

I think the amount of screen space these WM's provide and the time they save you fiddling with your windows is well worth the effort to set them up to your liking.

As stated earlier you can use compizconfig-settings-manager and if so you need the compiz-fusion-plugins-extra if it is not ready installed with the compizconfig-settings-manager package and if you have installed that plugin aswell you might need to activate it in: